Measuring the intensity of the light passing through a medium at specific wavelengths, one can determine the presence and concentration of various chemical and biological components. Absorption can be caused by a chemical reaction with an added reagent or by direct absorption by the molecules. Fluorescence can also be a powerful analytical tool, especially in biological detection. Dispersing the light into spectral components in a spectrograph, and then detecting the wavelengths of interest using an array of photodetectors can determine the intensities at specific wavelengths of interest. Commercial spectrometers using this principle are widely available in the visible range, largely due to the availability of chemical reagents, and inexpensive arrayed photodetectors (primarily charge coupled device (CCD) arrays). A schematic of a traditional detector array-based spectrometer is shown in with reference to FIG. 1A. In the infrared spectral regions, photodetector arrays are more costly and prone to thermal noise. To reduce cost or improve sensitivity, several other techniques have found use in commercial instruments. These include Hadamard Transform Spectrometers, Fourier Transform Spectrometers, and monochromators. Both Hadamard and Fourier transform spectrometers require longer measurement times and computing power in exchange for improved sensitivity. The monochromators use mechanically scanned slits or gratings to measure a single frequency at a time; measurement of a variable passband width would require changing slits, and measurement of noncontiguous wavelength bands is not practical. Often analytical techniques can benefit from instantaneous or time-resolved measurements, making serially read detector arrays and the aforementioned time-integrated techniques less relevant.
In a different type of spectrometer, one can use a programmable mirror array to direct only the desired wavelengths onto a single detector. MEMS mirrors can allow rapid reconfiguration of the desired spectral passbands, and the detector may be selected based on cost, sensitivity, response speed requirements, etc. This layout would be especially useful in industrial, consumer, and military applications where an instrument is needed to make repeated measurements (e.g. absorption at a specific wavelength) of fixed spectral bands, while allowing fast and re-programmable configuration. Such a system is illustrated in FIG. 1B. The benefit of this type of spectrometer is that only the wavelengths of interest are measured, and since the number of detectors is reduced, it can be a more specialized type. For example, a fast sensitive detector could be used to provide time-resolved fluorescence measurements.
One of the primary challenges for making such a system is a reconfigurable micromirror array capable of deflecting incident light onto or away from a detector. Accordingly, what is needed in the art is an improved system and method for the control of a MEMS-fabricated electrostatic array.